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Accuracy of Rapid Strep Testing vs. Throat Culture

Am Fam Physician. 2002 Dec 15;66(12):2297.

The development and continued evolution of streptococcal antigen testing has provided physicians with a rapid technique for determining which patients with acute pharyngitis are infected with group A beta-hemolytic streptococcus. Streptococcal antigen testing has improved the appropriateness of antibiotic use and provided physicians with earlier laboratory confirmation of streptococcal pharyngitis. This antigen test provides physicians with more accurate information about streptococcal pharyngitis because, despite multiple attempts at diagnostic scoring systems and methods, clinical criteria for identifying streptococcal pharyngitis are not reliable. The reliability of the rapid streptococcal antigen test is an important factor to determine, particularly in patients with a recent history of group A beta-hemolytic streptococcal pharyngitis. Sheeler and colleagues determined the accuracy of the rapid streptococcal antigen test in patients who had been treated recently for streptococcal pharyngitis.

The trial was a prospective study of two groups. The first group included patients who were diagnosed with acute streptococcal pharyngitis within the past 28 days. The control group included patients with sore throat but without a diagnosis of streptococcal pharyngitis within the past 28 days. Pharyngitis was defined as the subjective complaint of sore throat and dysphagia, with or without fever or malaise, and the objective presence of tonsillar exudates. The population studied was a continuous sample of patients presenting to an urgent care center. All patients who met the criteria received a rapid streptococcal antigen test and a throat culture. Data collected included recent history of streptococcal pharyngitis, type of antibiotic used in those with a history of infection, and results of the testing.

The total number of observations included in the study was 443, with 211 having received antibiotics for streptococcal pharyngitis. The rapid streptococcal antigen testing showed no difference in specificity when compared with throat culture results (0.96 versus 0.98). In addition, the study revealed that the rapid antigen test was more reliable than throat cultures in patients who had recent streptococcal pharyngitis. The false-positive and false-negative rates for the antigen test and throat culture were similar.

The authors conclude that rapid streptococcal antigen testing is sensitive and specific in patients who have a history of recent streptococcal pharyngitis. This finding allows physicians to treat patients with streptococcal pharyngitis earlier and will reduce symptom duration and number of days of bacterial shedding.